This proposal outlines a plan to develop a validated high throughput screen for inhibitors of RNA-protein complex formation by two STAR proteins: GLD-1 and Quaking. The ultimate goal will be to configure these assays for submission to the MLSCN for a large scale screening effort. GLD-1 is a regulatory of germline development in C. elegans, and Quaking is a mouse protein that regulates myelination in the developing nervous system. The STAR protein family is an important class of RNA binding proteins that also includes Sam68 and the SLM proteins that are implicated in a wide variety of processes, and is linked to certain types of cancer. A fluorescence polarization assay will be developed that monitors the change in polarization of a fluorescently labeled RNA upon binding to the protein. Small molecule competitors will be identified by screening for decreases in polarization. Such validated inhibitors would be powerful tools for functional studies in C. elegans and mice, and the assay should be readily extended to inhibitors of Sam68 once suitable RNA targets have been identified.